Exposure to genistein during gestation and lactation demasculinizes the reproductive system in rats

Purpose: Exposure to the phytoestrogen genistein (Indofine Chemical Co., Somerville, New Jersey) can disrupt normal male sexual differentiation. To determine if perinatal (that is gestation and lactation) genistein exposure at doses common in human diets alters masculinization we examined the development of the external genitalia, testes, wolffian ducts and sexual behavior in male rats exposed to genistein supplemented diets during early development. Materials and Methods: Female rats were fed a phytoestrogen-free diet supplemented with no genistein (free), a low genistein dose (low) or a high genistein dose (high) throughout gestation and lactation. Anogenital distance of male offspring was measured weekly from postnatal days 2 to 21. At puberty (postnatal day 40 to 45) preputial separation, and testis length and width of male offspring were measured. At age 70 days reproductive organ masses, plasma testosterone concentration, sperm counts and sexual behavior were assessed in male offspring. Results: Exposure to genistein resulted in temporary, prepubertal urogenital abnormalities at postnatal days 21 and 40. Males exposed to genistein had smaller anogenital distance and testis size, and delayed preputial separation. Perinatal exposure to genistein also caused long-term dysfunction in reproductive behavior, in which adult males exposed to genistein were less likely to mount, intromit and ejaculate during mating tests. Males exposed to genistein also had lower testosterone concentrations in adulthood. Conclusions: Perinatal genistein exposure results in transient and lasting alterations in masculinization of the reproductive system. These results extend our knowledge of the effects of early genistein exposure on male development and may have implications for human health in terms of potential relationships of endocrine disrupters and urogenital abnormalities thought to be increasing in incidence in boys and men.